They probably have triple buffer enabled or something.

There's 33ms extra lag due to the deflicker routine. Anything lower and you'll get glitches, especially in the SM5A games. On other games too, I had glitches in Mario Bros and TMNT for example before adding deflickering.
Also, the fake SVG screen runs at 60hz so any LCD changes sent as outputs to MAME's SVG screen will have a lag of max 16ms.

So, I guess on average 40ms + whatever lag MAME+OS already has.

Perhaps having the deflicker be handled by a shader that simulates the LCD persistance would prevent some of that lag?

What deflicker is mostly trying to prevent here (and what the lag is caused by) is a delay from segment-off to segment-on.
(On to off too, aka persistance, but that isn't what's causing the lag)

eg. game strobes LCD segment for a few milliseconds, it won't be visible on the real thing. On MAME without this deflicker, you'd get unwanted segments showing up.

Space Bridge, a Soviet G&W Fire clone by Elektronika, has been preserved in MAME

The ROM data has been verified to exactly match the original game. The gameplay is exactly the same but graphics is slightly changed and the setting is changed to a space theme. This is what the game looks like:



Scans of the game case and LCD background has been uploaded to the dropbox dir.

Thanks to JustDesserts for lending out the game!